Vitamin D and K2 Together: Reading Combination Products

A large share of vitamin D supplements now include vitamin K2, and the pairing is marketed as though it were a single ingredient. On the label they are two separate nutrients with two separate doses, and the second is frequently much smaller than the packaging implies.

What K2 is

Vitamin K exists as K1 (phylloquinone), found in green leafy vegetables, and K2 (menaquinone), which occurs in several sub-forms. Supplement labels usually specify MK-4 or MK-7 — these are different menaquinones with different properties, and a product that says only “K2” is telling you less than one that names the sub-form.

How to read a combination panel

Look for four things:

1. The vitamin D dose, in IU or mcg — see converting the units.
2. The vitamin D form, D3 or D2 — see D3 vs D2.
3. The K2 dose in micrograms, which is a much smaller number and easy to skim past.
4. The K2 sub-form: MK-7 or MK-4.

The interaction that matters

Vitamin K interacts with warfarin and other vitamin K antagonist anticoagulants. This is a well-established, clinically significant interaction, and it is the single most important thing on this page. If you take warfarin, do not start a vitamin K-containing supplement without speaking to the clinician managing your anticoagulation — including a combined D and K2 product, where the K2 may not be prominent on the front of the bottle.

If you take an anticoagulant and want vitamin D, a plain vitamin D product without K2 avoids the question entirely.

Is the combination necessary?

That is a clinical question rather than a labelling one, and the honest answer is that it is an area of ongoing research rather than settled advice. What we can tell you is what a given bottle contains and at what dose, which is what our vitamin D comparison is for.

References

• NIH Office of Dietary Supplements — Vitamin D (Health Professional Fact Sheet)
• NHS — Vitamin D
• NIH Office of Dietary Supplements — Vitamin K